The present invention relates to an electroluminescent device (hereinafter referred to as xe2x80x9cEL devicexe2x80x9d) having a luminescent layer comprising luminescent particles and a matrix resin. In particular, the present invention relates to an EL device with high luminance which is based on the concept different from that of conventional xe2x80x9cdispersion type luminescent layersxe2x80x9d.
EL devices comprising a so-called xe2x80x9cdispersion type luminescent layerxe2x80x9d which is formed by dispersing luminescent particles such as fluorescent substances in a matrix resin such as a polymer having a high dielectric constant are known from the following publications:
For example, JP-B-59-14878 discloses an EL device comprising a transparent substrate, a transparent electrode layer, an insulating layer consisting of a vinylidene fluoride base matrix resin, a luminescent layer comprising a vinylidene fluoride base matrix resin and fluorescent particles, the same insulating layer as above, and a rear electrode, which are laminated in this order.
JP-B-62-59879 discloses an EL device comprising a polyester film, an ITO electrode, a luminescent layer comprising a cyanoethylated ethylene-vinyl alcohol copolymer (a matrix resin) and fluorescent particles, and an aluminum foil (a rear electrode), which are laminated in this order.
However, such the xe2x80x9cdispersion type luminescent layersxe2x80x9d can hardly increase the luminance, because the luminescent particles having a larger specific gravity than the matrix resin tend to sink in a paint for forming a luminescent layer comprising the luminescent particles dispersed in the matrix resin solution and therefore, it is difficult to disperse the luminescent particles uniformly in the matrix resin in the luminescent layer formed from such the paint.
Furthermore, the dispersibility deteriorates when the amount of the luminescent particles in the paint is increased for increasing the filling rate of luminescent particles in the luminescent layer. Thus, the added amount of the luminescent particles is limited.
In addition, it is relatively difficult to increase a coating thickness of the luminescent layer with a uniform thickness using such the dispersion type paint. Therefore, the number of applications of the paint should be increased to increase the thickness of the luminescent layer for increasing the luminance, the productivity decreases, and it is difficult to produce a sheet-form EL device having a large area.
One object of the present invention is to provide an EL device with an increased filling rate of luminescent particles in a luminescent layer and significantly improved luminance for solving the above problems of the conventional devices.
Another object of the present invention is to provide a method for producing an EL device which can produce a sheet-form EL device having a high luminance and a large area at a high productivity without using the above dispersion type paint.
According to the first aspect (and with reference to FIG. 1.), the present invention provides an electroluminescent device comprising:
a) a transparent substrate (1),
b) a transparent conductive layer (2) placed on the back surface of said transparent substrate (1),
c) a luminescent layer (8) comprising luminescent particles (7) and a matrix resin and being placed on the back surface of said transparent conductive layer (2), and
d) a rear electrode (6) placed on the back surface of said luminescent layer (8),
wherein said luminescent layer (8) comprises
(c-1) a transparent support layer (3) comprising a matrix resin and being placed on the side of said transparent conductive layer (2),
(c-2) an insulating layer (5) comprising an insulating material and being placed on the side of said rear electrode, and
(c-3) a luminescent particle layer (4) consisting essentially of particles which comprise luminescent particle (7) and are embedded in both said support layer (3) and said insulating layer (5).
According to the second aspect, the present invention provides a method for producing an electroluminescent device which comprises a transparent substrate (1), a transparent conductive layer (2) placed on the back surface of said transparent substrate (1), a luminescent layer (8) comprising luminescent particles (7) and a matrix resin and being placed on the back surface of said transparent conductive layer (2) and a rear electrode (6) placed on the back surface of said luminescent layer (8), which method comprises the steps of:
i) providing a transparent substrate (1) on one surface of which a transparent conductive layer (2) is laminated,
ii) applying a paint for forming a support layer (3) containing a matrix resin on said transparent conductive layer (2),
scattering particles containing luminescent particles (7) in a layer state and embedding a part of each particle in said paint prior to solidification of said paint,
solidifying said paint and forming a transparent support layer (3) and a luminescent particle layer (4) bonded to said support layer (3),
iii) applying a paint for forming an insulating layer (5) comprising an insulating material on said luminescent particle layer (4), solidifying said paint and forming said insulating layer (5) bonded to said luminescent particle layer (4), and
iv) laminating a rear electrode (6) on said insulating layer (5).
In the EL device of the present invention, the luminescent particle layer (4) contained in the luminescent layer (8) comprises substantially the particles containing the luminescent particles, and is placed between the support layer (3) and the insulating layer (5) and bonded to the both layers. Therefore, the filling rate of the luminescent particles in the luminescent layer (8) increases, and the luminance increases considerably.
Furthermore, when the EL device is produced by the method of the present invention comprising the steps i) through iv), it is not necessary to use the dispersion type paint of luminescent particles unlike the conventional techniques, and the sheet-form EL device having the high luminance and the large area can be produced at a high productivity.